One advantage of traditional film photography over digital photography is the flexibility of its associated photofinishing process. In photofinishing, exposed film is developed, a piece of light-sensitive photographic paper is exposed through the resulting negative, and the exposed photographic paper is processed through a series of chemical solutions to produce the finished print. There is considerable flexibility in how the photofinisher or photographer develops the film (e.g., push processing), and the exposure of the photographic paper can be varied to take advantage of the wide dynamic range inherent in film.
In contrast, digital cameras typically perform the equivalent of this photofinishing step inside the camera itself. In a digital camera, an imaging sensor such as a charge-coupled device (CCD) initially produces an uncompressed digital image that is normally compressed by a significant factor in conformance with a standard such as that of the Joint Photographic Experts Group (JPEG). Prior to compression, most digital cameras also perform one or more adjustments on the uncompressed image. For example, the digital camera may correct the exposure or adjust the color balance or tone reproduction of the uncompressed image. Compression also often involves converting the uncompressed digital image from one color space to another (e.g., from RGB to YCrCb). In compression, a tremendous amount of information is lost. For example, the output of the CCD in a 5-Mpixel digital camera is typically interpolated to 15 Msamples to compensate for the CCD's mosaic pattern (i.e., to supply missing color information). Each sample may be, for example, 10, 12, or 14 bits long. This large uncompressed image, following the aforementioned adjustments, is subsequently compressed to approximately one-half to one Mbyte. When a user attempts to post-process the compressed digital image further (e.g., adjust tone reproduction, color balance, etc.), compression artifacts may become visible. Also, although the dynamic range of the original uncompressed image is fairly large, it is still not as wide as that of film. Thus, even though some digital cameras support saving a digital image in uncompressed form, the post-processing a user can perform on the uncompressed image is still somewhat limited.
It is thus apparent that there is a need in the art for an improved method and apparatus for producing digital images.